1. Field of the Invention
The present invention relates to a hydraulic tensioner lifter of a tensioner for applying tension to an endless power transmission band such as a chain or a belt used for a power transmission mechanism, for example, in an internal combustion engine.
2. Description of Background Art
Conventionally, in an internal combustion engine, a hydraulic tensioner lifter is used in order to apply suitable tension to an endless power transmission band used for a power transmission mechanism such as, for example, a chain. In this hydraulic tensioner lifter, an oil chamber is formed between a plunger biased by a tensioner spring for applying tension to a chain and a tensioner body, and oil pressure is supplied into the oil chamber through a check valve. If a slack occurs with the chain during operation, then the plunger is advanced outwardly from the tensioner body by the resilient force of the tensioner spring, and oil pressure flows into the oil chamber to apply tension to the chain. On the other hand, if the chain is tightened and a load in a direction in which the plunger is to be retracted acts upon the plunger from the chain, then the oil pressure in the oil chamber stops the retreating movement of the plunger to suppress vibration of the chain.
Incidentally, when the internal combustion engine stops, a supply of oil pressure into the oil chamber of the tensioner lifter stops, and therefore, as time passes, the oil pressure in the oil chamber gradually leaks through a very small gap between sliding portions of the plunger and the tensioner body and so forth, whereupon air is admitted into the oil chamber. Accordingly, upon starting of the internal combustion engine, when oil pressure is to be supplied into the oil chamber which is not filled with oil pressure, preferably air in the oil chamber is exhausted rapidly in order to allow the vibration-damping function of the tensioner lifter to be exhibited at an early stage.
Thus, for example, in a hydraulic tensioner (which corresponds to a tensioner lifter) disclosed in the official gazette of Japanese Patent Laid-Open No. 2000-240744, a housing (which corresponds to a tensioner body) which cooperates with a plunger to define a high oil pressure chamber therebetween includes an orifice member provided therein in which an orifice communicated with an upper portion of the high oil pressure chamber is formed. If the plunger which is biased by a plunger spring (which corresponds to a tensioner spring) to project to the outside of the housing is acted upon by an impact, a load or the like in a direction in which the plunger is to be retracted from a chain and the oil pressure in the high oil pressure chamber rises, then air or oil in the high oil pressure chamber leaks through the orifice thereby to moderate the impact upon the plunger from the chain or the like.
Incidentally, in the prior art described above, since the orifice is in communication with the upper portion of the high oil pressure chamber, it is considered that air admitted into the high oil pressure chamber is exhausted from the high oil pressure chamber by oil pressure supplied into the high oil pressure chamber upon the starting of the internal combustion engine. According to this, the high oil pressure chamber is quickly filled with oil pressure. However, since the high oil pressure chamber is normally communication with the outside of the high oil pressure chamber through the orifice, also after the air is exhausted, the oil flows out from the high oil pressure chamber through the orifice. Therefore, the filling time becomes long. In addition, if the chain becomes slackened and the plunger quickly advances outwardly, then the high oil pressure chamber is sometimes momentarily brought into a negative pressure state from the relationship to the viscosity of the oil pressure and the oil feeding rate into the high oil pressure chamber. In such an instance, there is the possibility that the external air may be admitted into the high oil pressure chamber through the orifice.
Japanese Patent Laid-Open No. 2000-240744 also includes an accommodation hole formed therein with a plunger fitted for sliding movement in the accommodation hole and cooperating with the housing to define a high oil pressure chamber therebetween. A plunger spring is disposed in the inside of the plunger for biasing the plunger so that one end portion of the plunger may project outwardly from the housing. Further, a check valve mechanism for supplying oil into the oil chamber from a feed oil path provided in the housing is provided at a bottom portion of the accommodation hole, and a relief valve is provided on the outward projection side of the plunger. The relieve valve is composed of a sleeve provided for sliding movement in an orifice member force fitted in the plunger, and an outflow exit formed in the orifice member. Further, the plunger spring is disposed between the bottom portion of the accommodation hole and the plunger in the proximity of an end face of the orifice member adjacent the oil chamber. Furthermore, rather near to the end of the plunger, an oil reservoir chamber into which oil flowing out from the outflow exit of the relief valve flows is formed between the orifice member and the plunger, and a plug having a discharge port for discharging oil in the oil reservoir chamber to the outside of the tensioner is provided at the end of the plunger.
Further, in the tensioner described above, if a slack occurs with the chain which is operating, then the plunger projects from the housing by the resilient force of the plunger spring and oil pressure flows into the oil chamber through the check valve mechanism to apply tension to the chain. On the other hand, if the chain becomes tight and a load in the direction in which the plunger is retracted acts upon the plunger, then the oil pressure in the high oil pressure chamber resists the retreating movement of the plunger so that suitable tension may be applied to the chain while suppressing the vibration of the chain. Further, if the plunger is acted upon by a load in the retreating direction from the chain and the oil pressure in the high oil pressure chamber rises excessively, then the relief valve operates and the sleeve moves against the sleeve spring to open the outflow exit so that the oil in the high oil pressure chamber flows out from the outflow exit thereby to prevent an excessively high oil pressure from being generated in the high oil pressure chamber. Then, the oil flowing out from the outflow exit flows into the oil reservoir chamber and then is discharged from the oil reservoir chamber to the outside of the housing through the discharge port.
Incidentally, when the internal combustion engine stops, no oil is supplied into the oil chamber of the tensioner lifter, and therefore, as the time passes, the oil in the high oil pressure chamber gradually leaks through sliding portions of the plunger and the tensioner body and so forth, whereupon the amount of the oil in the high oil pressure chamber decreases and air is admitted into the high oil pressure chamber. Therefore, upon starting of the internal combustion engine, the vibration-damping function of the tensioner acts after the oil chamber is filled with oil. However, in the prior art described above, since the plunger spring is disposed between the bottom portion of the accommodation hole and the plunger in the proximity of the end face of the orifice member adjacent the oil chamber, as the volume of the high oil pressure chamber increases, the filling time until the high oil pressure chamber is filled with oil after oil in the oil chamber leaks becomes long.
Further, in the prior art described above, in order to discharge oil in the high oil pressure chamber to the outside of the tensioner through the relief valve, the oil reservoir chamber formed from the plunger and the plug provided at the end of the plunger are required. Therefore, a great number of steps for assembly of the mechanism for discharging oil to the outside of the tensioner are required. Further, in order to discharge oil from the outflow exit of the relief valve to the outside of the tensioner, it is necessary to form the oil reservoir chamber and the discharge port. Therefore, a large size is required for the plunger and hence for the tensioner.